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A recent BBC news article give a short history on the canals of Mars

In the late 19th Century, the American astronomer Percival Lowell thought he saw canals on the surface of Mars.

He suggested that this was evidence that our near planetary neighbour might not only harbour life, but could possibly be home to an advanced civilisation.

This fired the public's imagination - prompting HG Wells's novel, The War of the Worlds, several comics and numerous Hollywood science fiction films depicting Martian invasions.

There was a mixture of disappointment and some relief when the existence of canals was finally disproved by orbiting spacecraft sent to the Red Planet in the 1960s and 70s.

Note: There are a number of other significant series, including John Carter of Mars and the Barsoom Series that began in 1912 by Edgar Rice Burroughs in which the canals played a major part.

If there are no canals on Mars now, what was it that everyone was seeing that created and continued the belief in the Martian Canals?

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    $\begingroup$ If nobody answers by the time I'm home, I will write this up: Carl Sagan talked about this in one of his books. If I remember correctly, he attributed it to two things: The first is a mass delusion, where figures of authority claim to see the canals. The second is human pattern recognition falsely seeing lines in loosely-aligned streaks of craters. $\endgroup$
    – Rikki-Tikki-Tavi
    Oct 2, 2015 at 13:06
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    $\begingroup$ I saw a lecture online by astronomy historian Owen Gingrich where he said that Lowell agreed to other astronomers' proposal to observe a ball painted with a hypothetical geography, from a distance through a telescope, and draw what he saw. Sounds like a reasonably scientific method to me. He failed those tests and refused to continue them. Sorry that I have no source since video content is hard to search. Worthwhile to watch all you find by Owen anyway. Lowell built the world's largest telescope with his own money, kind of an Elon Musk of his day I suppose, which gave him credibility. $\endgroup$
    – LocalFluff
    Oct 2, 2015 at 14:04
  • $\begingroup$ I don't have a source for this so I'll just leave a comment - I saw a theory years ago that suggested the problem was a combination of extreme magnification, very small exit pupil, and "streaks" caused by the blood vessels on our own retinas! Certainly those wiggly lines from blood vessels are familiar to those of us who get regular eye exams... $\endgroup$
    – Andy
    Oct 2, 2015 at 14:34

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Canals on Mars has quite an interesting history, starting with Giovanni Schiaparell. He produced this map of Mars in 1877

![enter image description here

It is interesting to compare this map to a more modern map

enter image description here

Note that the same general features are labeled, however, the lines that run between them don't show up at the modern image. Giovanni was Italian, and called the lines on these chart "canali", which means Channels. It was erroneously translated as Canals, a small, but significant different, canal implying produced by something. This false believe became quite popular, and fed upon itself, becoming something more than it really was.

The current theory as to why these channels were seen is that they were optical illusions, followed by the expectation that there should be canals, and nothing more. Keep in mind that the images used to produce such maps looked something like this:

enter image description here

It's amazing that he was as accurate as he was! The channels as seen were simply too small to be accurate, however, and thus were simply optical illusions.

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This article about canals on Mars says:

More recent scholarship suggests that what Percival Lowell observed as Martian canals was merely observing projections of the vein structure of his own eyeball, a known nuisance among planetary observers using very high magnification."

(links added and text bolded by me)

IOW, it was artifact of poor instrumentation they used at that time.

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  • $\begingroup$ I had a similar issue with microscopes - I can see viruses and things that are in my eye that I thought were on the slide. $\endgroup$
    – Hannover Fist
    Oct 2, 2015 at 20:46
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    $\begingroup$ So he's up to his eyeballs in his work, eh? sensible chuckle $\endgroup$
    – corsiKa
    Oct 2, 2015 at 20:59
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    $\begingroup$ @HannoverFist You can see a virus in your eye?? $\endgroup$
    – LocalFluff
    Oct 3, 2015 at 1:07
  • $\begingroup$ @LocalFluff: Occasionally I see a floater in my eye. It's a little blur that looks very similar to objects under an optical microscope that isn't perfectly focused. $\endgroup$
    – David Cary
    Oct 3, 2015 at 13:24
  • $\begingroup$ @DavidCary Oh, yeah, I do too! Actually, an artistic class mate in elementary school made drawings of those elusive shapes he saw when he closed his eyes. He called them astronauts. If they are microbes, and not just some kind of brain malfunction, that would be fantastic. Closed eye observatory - can I get money for studying this full time :-D $\endgroup$
    – LocalFluff
    Oct 3, 2015 at 15:04

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